The present invention relates to a medical piercing cannula having a drip chamber, for use with a medical container such as a container of a fluid to be infused into a patient's body, and more particularly to a medical piercing cannula with a drip chamber, the medical piercing cannula having a fluid passage and an air passage which is associated with a regulating mechanism for regulating the rate of flow of air which enters the air passage.
When various fluids containing nutrients such as amino acids, vitamins, or the like, hemostatics, and anesthetics, and artificial blood are infused into patient's bodies by way of intravenous drip, these fluids are supplied from medical containers or bottles in which they are sealed. The fluid contained in such a medical container is introduced into a fluid conduit through a medical piercing cannula inserted into the container.
Some conventional medical piercing cannulas for use with medical containers or bottles have air passages. The medical containers of fluids with which medical piercing cannulas are used are grouped into hard containers such as glass bottles which are rigid and do not change their shape and soft containers such as fluid storage bags which are flexible and can change their shape.
When a medical piercing cannula is joined to a hard medical container in order to withdraw the contained fluid, such as a drug solution, therefrom, it is necessary to supply air through an air passage in the needle into the container so that the fluid can smoothly be evacuated from the container through replacement with the introduced air. The rate of flow of the fluid from the hard container is regulated depending on the rate of flow of air from the air passage into the hard container.
The prior medical piercing cannulas for use with medical containers are constructed such that their air passages can be closed off as desired so that they can be used with both hard and soft medical containers.
More specifically, the known medical piercing cannulas of the above type are classified into:
(1) medica piercing cannulas having air passages which can be closed off by caps or plugs in openings of the air passages; PA1 (2) medical piercing cannulas having air passages whose openings can be adjusted in cross-sectional area by rotatable caps in the openings (see Japanese Laid-Open Utility Model Publication No. 56(1981)-80149); and PA1 (3) medical piercing cannulas having air passages with check mechanisms disposed in openings thereof (see Japanese Utility Model Publications Nos. 49(1974)-3187, 50(1975)-13428, 50(1975)-56096, and Japanese Laid-Open Patent Publication No. 51(1976)-63586).
According to the medical piercing cannulas under the category (1) above, the caps or plugs are connected to the cannulas through strings or the like so that they will not be lost after they are removed from the openings of the air passages. When such medical piercing cannulas are used, these caps or plugs tend to interfere with the user. In addition, the caps or plugs cannot smoothly be removed from or fitted into the openings.
The medical piercing cannulas of the class (2) above can be used with flexible soft containers when the air passages are closed off by turning the caps. When a medical piercing cannula of this class is used with a hard container and the cross-sectional area of the opening of the air passage is reduced by the cap, it is possible to prevent the fluid from gushing out of the hard container, but it is impossible for the user to accurately know how the fluid is being dripped. Consequently, it is difficult to regulate the rate at which the fluid is supplied from the hard container, i.e., the rate of dripping of the fluid from the hard container.
The check mechanisms associated with the air passages in the medical needles in the group (3) above are in the form of check valves. When a medical piercing cannula of this type is used with a flexible soft container, the check valve operates to prevent the fluid from flowing out of the container. One problem with these check valves is that when particles of dust or residues of the fluid are jammed in the check valve, the check valve tends to become ineffective, and the fluid in the soft container may egress from the air passage.